The areas below waterfalls, both big and small, can be great places to seek out big trout. This should come as no surprise. Typically referred to as plunge pools, the water that sweeps over falls and into these pools continuously delivers all manner of food to fish waiting below. In areas where the plunging water is pinched or otherwise funneled by the structure of the stream, falls not only deliver food that has swept down from above but also produce a concentrated, high density stream of that food. The turbulent nature of water on the surface of a plunge pool serves to obscure and conceal everything below, providing excellent cover from predators. And despite the turbulent, often violent currents at the surface of these pools, the deep, sometime boulder-filled recesses below offer respite from strong currents.
Don't Pass Them By
Bigger trout push smaller trout out of prime lies. That's the way it goes. So, the fact that these pools offer up a bounty all of a trout's most important needs: cover, food and protection from currents, makes them prime lies. This, in turn, means that they will commonly hold some of the best trout in the stream. Still, I've seen many a fisherman pass them by or ply them only momentarily, put off by the chaotic nature of the water's flow or unwilling to strap on 14 pieces of split shot in order to get their fly down to the fish hiding below.
The first of those two common put-offs is sort of a misconception, as water at the bottom of a plunge pool is typically calm and serene compared to the water above. The second, the inability to get a fly down to the bottom of a plunge pool without bowling balls strapped to your leader, is simply a matter of employing the wrong approach.
Plunge pools, for all of the reasons mentioned thus far, should rarely -- if ever -- be passed over.
Accessing the Plunge Pool
The instinct of most, but certainly not all, fly fisherman when fishing plunge pools seems to be to cast into the bubbling, turbulent water below the falls. Often, these casts are delivered right to where the plunging water meets the surface below. As experience will eventually reveal, this is the hardest place at which to attempt to deliver a fly to the water below.
The boiling water below a waterfall is just so because of air, swept below by the diving water, rising back to the surface. The result is a strong upcurrent which virtually any normal nymph rig will be powerless to resist. Casting into this area will result in little more than a fly that never travels far from the surface and one that is obscured by the rough, agitated water.
Thankfully, getting your flies down into prime lies in plunge pools doesn't require elaborate, heavily weighted rigs. Instead of delivering the fly into the tempestuous water at the bottom of the plunge, cast directly into the plunge or just above the plunge. Just as the air that boils back to the surface is swept to the bottom of the pool, so too will your fly be, hopefully right into the field of vision of waiting fish.
One of my favorite plunge pool tactics is to toss a woolly bugger into the plunge, wait for it to get swept below and strip it to life at the bottom of its dive. I like to imagine that the bugger does a fair job of imitating a sculpin, terrestrial, large nymph or other hearty meal that was unsuspectingly swept over the falls and is trying to swim to shelter after getting tossed around by the current. More than a few nice trout have seemed to agree.